The present invention relates to a control technology of a magnetic disk storage system, and a technology effective when applied to motor control at the time of shut-off of a power supply like the time of the occurrence of power failure, e.g., a technology effective for use in retraction control of a magnetic head by a voice coil motor for moving the magnetic head that effects read/write of information on a storage track on a magnetic disk in a hard disk drive.
A magnetic disk storage system includes a voice coil motor for moving (seek-operating) a magnetic head that effects read/write of information on a storage track on a magnetic disk, in a radial direction along the surface of the magnetic disk in addition to a spindle motor for rotatably driving the magnetic disk. In a hard disk drive, the magnetic head is configured so as to glide on the surface of the disk with wind pressure developed with the rotation of the disk. Thus, there is a possibility that when the rotation of the disk is stopped, the magnetic head will come into contact with the disk surface to thereby make flaws thereon. There is further a possibility that when the disk surface is brought to a mirror state with an advance in high density of magnetic recording, the stopped head will be absorbed at the disk surface to thereby block the rotation of the disk.
Thus, when the rotation of the disk is stopped, the operation (called unloading in the present specification) of retracting the magnetic head to a support table called a ramp placed in a standby position lying outside the disk is performed. On the other hand, it is necessary to move (load) the magnetic head from the ramp position onto the disk at the seek start of the head. At this time, there is a possibility that when the speed of travelling of the magnetic head by the voice coil motor extremely increases, the magnetic head will make contact with the disk surface to thereby damage it. Therefore, it has generally heretofore been practiced to monitor a back electromotive voltage of the voice coil motor and control the travelling speed of the magnetic head.
The hard disk drive needs to retract the magnetic head as a matter of course even upon the occurrence of power failure from the reason similar to the necessity of retracting the magnetic head to the ramp placed outside the disk when the rotation of the disk is stopped. Since, however, a power supply for a control circuit of the voice coil motor is also shut off upon the occurrence of the power failure, it becomes unfeasible to drive and control the voice coil motor.
Thus, there has been proposed the invention wherein a retracting driver (hereinafter referred to as a retract driver) is provided aside from a driver (hereinafter called a VCM driver) for driving a voice coil motor for head seeking, and the retract driver is operated by a voltage obtained by rectifying a back electromotive force of a spindle motor upon the occurrence of power failure (see Patent document 1).
[Patent Document 1]
Japanese Unexamined Patent Publication No. Hei 7(1995)-14331.